"Thermodynamics and Nucleation Processes: Classical versus Generalized Gibbs Approaches".


Annotation

In the last decade, a new approach for the determination of the work of critical cluster formation in the description of
nucleation processes is developed. For an illustration, the method is applied in the discussion here to phase formation
processes in solid and liquid solutions. However, it is applicable quite generally and not restricted
to this particular important case. The present approach represents a generalization of the classical
Gibbs. method. It is.like the classical method.conceptionally simple and directly applicable to
real systems, but avoids its shortcomings. Central to our method was originally the formulation and application
of a new well-founded principle we denote as generalized Ostwald.s rule in nucleation. The method
allows the determination of the work of critical cluster formation provided the bulk properties and
the macroscopic values of the surface tension at planar interfaces for the possible different states
of the system under consideration are known. In the further advancement of the theory, this additional postulate is not
required since the theory gives then directly the same results.

 Similarly to the van der Waals.Cahn.Hilliard and density functional calculations in the determination of the work of critical
cluster formation, the newly developed method reproduces the results of the classical Gibbs. nucleation theory - involving the
capillarity approximation - for small values of the supersaturation. However, in contrast to the
classical and in agreement with van der Waals-type methods, for initial states approaching the
spinodal curve, the work of critical cluster formation, determined via the newly developed approach,
is shown to tend to zero. As an immediate additional consequence, the method gives a more accurate
description of the experimental results on nucleation rates also in the intermediate ranges of the
initial supersaturation. Some further implications for the theoretical interpretation of
nucleation-growth experiments are discussed as well.